Base64 Encoder & Decoder — Encode & Decode Free Online

base64 decode jwt token payload authorization

One of the most frequent uses of Base64 decoding in modern software development is inspecting JSON Web Tokens (JWTs). A JWT consists of three parts separated by periods (`.`): the header, the payload, and the signature.

The header and payload are both encoded using Base64URL format. If you need to debug authorization scopes or user IDs, you can simply copy the middle payload segment of the JWT and paste it into our decoder above (ensuring the URL Safe toggle is checked).

How Base64 Encoding Works Under the Hood

Base64 is a binary-to-text encoding scheme defined in RFC 4648. It translates raw binary data into a web-safe ASCII string representation consisting of 64 characters: A-Z, a-z, 0-9, +, and /.

At the bit level, standard computer bytes represent 8 bits of data. Base64 processes data by taking three 8-bit bytes (3 × 8 = 24 bits) and dividing them into four 6-bit chunks (4 × 6 = 24 bits). Each 6-bit numerical value maps directly to an index in the 64-character Base64 alphabet (2⁶ = 64).

Because four Base64 characters are required to represent every three raw input bytes, Base64 encoding increases overall payload file size by approximately 33%.

base64url vs base64 difference rfc 4648

Standard Base64 strings include + and / characters, which carry reserved structural meaning in URL paths and HTTP query parameters. To safely transmit payloads inside URLs, use the Base64URL variant.

javascript btoa atob utf8 unicode error

Modern web browsers natively support Base64 string manipulation via the btoa() and atob() window methods. However, because these legacy functions only support ASCII characters, passing emojis or UTF-8 strings directly will throw a DOMException error. Use the TextEncoder and Buffer APIs for safe Unicode handling:

// Browser Vanilla JS (Safe UTF-8 Unicode Encoding)
function encodeUTF8ToBase64(text) {
  const bytes = new TextEncoder().encode(text);
  const binary = Array.from(bytes, (byte) => String.fromCharCode(byte)).join("");
  return btoa(binary);
}

// Node.js Backend Implementation
const payload = "Hello, ToolForge! 🚀";
const encoded = Buffer.from(payload, "utf-8").toString("base64");
const decoded = Buffer.from(encoded, "base64").toString("utf-8");

convert file to base64 string linux terminal

If you are working in a CI/CD pipeline or a headless Linux server, you can encode files natively using coreutils without writing any code:

# Encode a configuration file and strip newlines
base64 -w 0 config.json > config_b64.txt

# Decode a string directly in the terminal
echo "SGVsbG8gV29ybGQ=" | base64 --decode